1. Field of the Invention
This invention relates to a system for controlling the temperature of an atomizer for an element analyzer.
2. Description of the Prior Art
There has been so far known a spectroscopic analyzer which is based on the Voigt effect or Zeeman effect, for example, as disclosed in the Japanese Patent Laid-Open No. 90871/76. Such an analyzer requires an atomizer to change a sample into its atomized vapor state. In the atomizer, in this case, the sample is heated to effect its conversion to the atomized vapor condition.
In a known system of controlling the temperature of such an atomizer, the current which flows through the heater (resistor) in the atomizer is adjusted to a predetermined value. In a further known system of this kind, a light sensor such as a photodiode which is provided in the vicinity of the external wall of the atomizer, is used to measure the intensity of radiant light emitted from the external wall of the atomizer in order to control the current through the atomizer. However, the former system has a defect in that, since the contact resistance between the atomizer and the associated electrodes used to supply current thereto changes with the atomizer condition, even keeping constant the current through the electrodes will cause a change in the atomizer temperature due to the heat developed at the contacts between the atomizer and the electrodes, whereby the exchange of the atomizer for a new one does not ensure that the new one will be placed under the temperature state at the time of the former. Further, the former system has another defect in that, since the wall of the atomizer becomes thinner as the atomizer is used, a constant current supplied to the atomizer will provide a temperature higher than a target temperature for the atomizer. On the other hand, in the latter system, it is also difficult to know accurately the temperature of the internal wall, since the external wall of the atomizer is different in temperature from the internal wall thereof. This is because the temperature of the external wall depends greatly upon the flow rate or velocity of the sheath gas. In addition, in the latter system, the external wall of the atomizer has a much longer life than the internal wall thereof, thereby providing a change in the emissivity of the external wall. This leads to such a defect that even if radiant light from the external wall is monitored accurately, it is difficult to control accurately the temperature in the atomizer.